Synthetic tanning agents and methods of preparation and use



April 1954 R. c. PUTNAM ET AL 2,676,870 7 SYNTHETIC TANNING AGENTS AND METHODS OF PREPARATION AND use Filed Oct. 24, 1951 2 Sheets-Sheet l Resorcinol Polyhydric phenol Phlorogluclnol 20% Solution in m| pu fs) Pyrogallol anhydrous organic Catechol solvent Et'her Hydroquinone propyl ether Di-isopropyl ether Di-N-propyl ether Alkyl Acetonitrile nitrile (I met part) Propionitrl'le Potassium cyanide Mercurlc cyanide Reflux Bubbled through mlxture.

hours Reacts with cyanide to form HCN.

Catalyzes simultaneous primary reactions between polyhydric phenol and both alkyl nitrite and HCN and also catalyzes concurrent condensation between primary reaction products.

Color develops and precipitate usually forms.

f'lg.

' Solution of Tanning Agent E Evaporate Dry or Solvent Extract ii 1 Tanning Tanning Inventors Agent Agent Robert C Putnam W'Zsorz M Klez'bac/rer April 27, 1954 R. c. PUTNAM ET AL 2,676,870

SYNTHETIC TANNING AGENTS AND METHODS OF PREPARATION AND USE Filed Oct. 24, 1951 2 Sheets-Sheet 2 lHide Ready for .Tanningl Alternate procedure\ Freeze or solvent dry Immerse Tanning 4-6 days Material of Invention 2% or more Dried Hide solution in |Q%-l5% moisture 2 Tanninq Methanol Immerse Material of Ethanol 4-6 Invention (may contain days 2% or more all solution in proportion of organic solvent water) Immerse for Tanned several E Hide hours i Etc. as in Conventional Tanned Hide Practlce l Etc. as in Conventional Practice F/gZ Inventors Robert C. Putnam Wilson M fYYeibac/rer- Patented Apr. 27, 1954 SYNTHETIC TANNING AGENTS AND METH- ODS OF PREPARATION AND USE Robert C. Putnam, Marblehead, and Wilson M. Kleibacker, Salem, Mass, assignors to United Shoe Machinery Corporation, Flemington, N. J., a corporation of New Jersey Application October 24, 1951, Serial No. 252,998

This invention relates to tanning and particularly to new tanning agents and to processes for making and tanning with the new agents.

The necessity for importing vegetable tanning materials, the slowness of their tanning action and their lack of uniformity have been responsible for a continuing search for synthetic replacements. Natural vegetable tanning materials have been analyzed and eiiorts have been made to reproduce the tanning action of these materials. Synthetic materials proposed and used as tanning agents have included watersoluble condensation products of formaldehyde with phenol or cresol sulphonic acids, or sulfonated condensation products of formaldehyde with phenol or cresol. In general, it has been found that although the materials heretofore developed have definite tanning properties, in practice these materials are useful only as auxiliary tanning agents.

Improved synthetic tanning agents are disclosed in the copending application of Robert C. Putnam and Agnes V. Bowles, Serial No. 260,772, filed December 8, 1951, entitled Tanning Agents and Methods of Forming and of Tanning with These Agents. Those tanning agents are reaction products of an aromatic ketone and an aromatic aldehyde which possess between them at least two hydroxyl groups. The tanning agents are effective to give well tanned leather products. However, preparation of these tanning agents calls for hydroxy aromatic ketones and aldehydes, some of which are difficult to obtain or expensive.

It is a feature of the present invention to provide new tanning agents prepared from readily available starting materials, the tanning agent being effective in accordance with the methods herein taught, to form a leather product having a high shrink point and a desirable softness and flexibility.

According to the present invention a polyhydric phenol is combined with an alkyl nitrile and a cyanide. Under acid conditions, as for example in the presence of hydrogen chloride, part of the polyhydric phenol reacts with the alkyl nitrile to form a hydroxy aromatic ketimine and another part combines'with HCN liberated from the cyanide to form an aromatic hydroxy aldimine. The ketimine and aldimine condense to form a reaction product which is the new tanning agent and which is believed to be a chalcimine substituted by hydroxyl groups on the aromatic nuclei.

The tanning process of the present invention based on the weight of the solvent;

19 Claims. (Cl. 8-94.33)

involves the treatment of skins or hides in the condition normally employed for tanning, for example in bated condition, which solutions of these reaction products and water to convert the skins or hides to soft flexible leather having a relatively high shrink point.

Reference is made to the attached drawings, in which Fig. 1 is a flow sheet of the steps of forming the new tanning agent of the present invention; and

Fig. 2 is a flow sheet of the steps employed in tanning with the new tanning agent.

The tanning agents of the present invention are ordinarily prepared by bringing together the reagents in solution in an anhydrous organic solvent such as ether, ethyl propyl ether, di-isopropyl ether and di-n-propyl ether in which hydrogen chloride is appreciably soluble. The reaction mixture will comprise a polyhydric phenol, an alkyl nitrile and a cyanide, usually a metal cyanide which reacts with acid to generate hydrogen cyanide. The polyhydric phenols which have been found useful in the preparation of tanning materials include resorcinol, phloroglucinol, pyrogallol, catechol, hydroquinone and. similar polyhydroxy aromatic compounds. These polyhydric phenols may be dissolved in the anhydrous solvent to the extent of approximately 20% This percentage is not critical but is a convenient concentration. To this solution an alkyl nitrile such as acetonitrile or propionitrile is added to the the extent of about one mol part to two mol parts of the polydric phenol. One mol part of a metal cyanide such as zinc cyanide, sodium cyanide, potassium cyanide and mercuric cyanide for two mol parts of the polyhydric phenol is added to the solution.

Hydrogen chloride gas is bubbled through the above mixture to generate hydrogen cyanide from the metal cyanide and to carry out the reaction between the reagents to form first the hydroxy aromatic aldimine and hydroxy aromatic ketimine and thereafter to form the reaction product believed to be a hydroxy substituted chalcimine. High temperatures are not required and it is usual to carry out the reaction at the reflux temperature which for ether may be around 35 C.

The reaction is considered complete after from about one to about eight hours, at the end of which time color has developed and a colored.

precipitate is usually formed. Precipitates are removed by filtration. A product possessing tanning properties may be recovered from filtrates directly by evaporation of solvent or by solvent extraction and decantation procedure. The pr cipitates recovered also possess tanning properties.

Tanning solutions are prepared by dissolving two or more percent, preferably four percent, of the tanning agent in a suitable solvent. Watersoluble materials may be dissolved in water. Water-insoluble products are dissolved in suitable organic solvents such as methanol or ethanol to which, if desired, a proportion of water not sufficient to precipitate the tanning agent may be added.

Skins or hides of animals generally used for making leather may be treated according to the process of the present invention. In the specification the terms skin or skin material are to be understood in their broad sense as including these materials. The term hide in the claims is intended to include both skins and hides in the condition in which they are normally employed for tanning treatment. Where organic solutions of the tanning agents are to be employed, skins or hides are dried by known solvent or freeze drying methods to a moisture content of about to based upon the weight of the hide after subjection to a further drying for sixteen hours in air at 105 C. It has been found that drying is most satisfactorily accomplished by the action of water miscible volatile organic solvents, for example, acetone, methyl acetate, isopropyl alcohol, dioxane, methyl Cellosolve acetate or other solvent which will remove the water without seriously harming the skin. This drying may be effected by leaving the skin immersed in an agitated bath of the solvent overnight. The solvent is then removed from the skin, suitably by evaporation in a stream of dry, warm air.

The skins or hides are then immersed in the tanning bath and subjected to a tanning treatment for a period depending upon the activity of the tanning agent and the thickness and denseness of the hide. In general, the tanning period may be from four to six days. Thereafter the skins or hides are removed from the tanning bath and immersed in water for a period of several hours. The tanning of the skin or hide is complete at this point and the tanned material may be subjected to such further treatment as desired.

Where aqueous solutions of the tanning agent are to be employed, it is not necessary to dry the skins or hides before treatment nor is a subsequent water treatment required to complete the tanning of the skin or hide, although, naturally the skin or hide will ordinarily be washed to remove excess tanning agent, salts, acids and the like.

The following examples are given as of possible assistance to aid in understanding the invention, but it is to be understood that the invention is not restricted to the reagents or conditions set forth:

Example I .-l5.8 gms. of phloroglucinol (0.125 mol), 2.05 gms. of acetronitrile (0.05 mol), 5.9 gms. of zinc cyanide (0.05 mol) and 100 cos. of dry ether were introduced into a reaction vessel. The mixture was heated to reflux temperature and subjected to continuous stirring at this temperature for eight hours during which time dry HCl gas was passed through the mixture. During the course of this heating the mixture developed a deep yellow color followed by the form t- 4 tion of an orange precipitate. The precipitate was removed by filtration and the filtrate concentrated by evaporation of the ether. The pre cipitate was refluxed with dry ether and undissolved portions again removed by filtration, the filtrate being combined with the original filtrate.

The combined ether filtrates were evaporated leaving a crystalline residue slightly darker than the original ether-insoluble precipitate.

Four percent solutions of the crystalline residue from the evaporation of the filtrate and of ether-insoluble material were prepared. Piece-s of bated hide dried by treatment in acetone to a moisture content of about 12% were placed in the 4% methanol solutions and kept therein for five days at room temperature. The pieces were then removed and placed in distilled water for 18 hours. Upon removal and drying of the hide pieces, the pieces were found to resemble leather and to be soft and flexible. A shrinkage point of 72 C. was found for the hide tanned with the ether-insoluble component and a shrinkage point of 75 C. was found for the piece tanned with the ether-soluble component.

Example II.-15.8 gms. of pyrogallol (0.125 mol), 2.05 gms. of acetonitrile (0.05 mol), 5.9 gms. of zinc cyanide (0.05 mol.) and 100 cos. of dry ether were placed in a reaction flask. The mixture was heated to reflux temperature and held at this temperature for five hours while the mixture was stirred and dry HCl gas was passed through it. At the end of this time the reaction mixture was filtered and the ether-insoluble solid component separated by filtration was rinsed with anhydrous ether. The combined ethereal solutions were allowed to evaporate to dryness. Both the material separated by filtration and the residue from the evaporation of the ethereal solutions had a dark red color.

A four percent solution of the ether-insoluble solid material in methanol was made up and used for the tanning of a piece of dried bated hide as in Example I. The product thus tanned had a shrink point of 81 C.

An aqueous solution containing four percent by weight of the ether-soluble component was made up; and a piece of bated steer hide immersed therein for a period of five days. At the end of this time the piece of hide was removed and washed to remove excess reagent. This piece, when dry, exhibited a shrink point of C. by the standard shrink test.

Example III.-13.7 gms. of resorcinol, 5.9 gms. of zinc cyanide, 2.05 gms. of acetonitrile and 100 cos. of dried ether were placed in a reaction flask and dry HCl gas passed through the mixture. The mixture was brought to reflux temperature and stirred for a period of five hours. After standing over night th reaction mixture separated into two layers, an ether-soluble layer and an ether-insoluble layer separated by decantation.

The ether-soluble portion was placed in an evaporating dish and the ether permitted to volatilize leaving a dry residue.

A four percent aqueous solution of the residue from evaporation of the ether-soluble material was prepared and used for the tanning of a piece of bated steer hide. A tanning period of five days was employed at the end of which time the hide was removed from immersion in the solution, washed and dried. The dried hide had a good feel and was flexible. On the conventional shrink test a shrink point of C. was obtained.

Having described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. A process for forming tanning agents which comprises bringing together a polyhydric phenol with both an alkyl nitrile and hydrogen cyanide and causing them to react in th presence of hydrogen chloride.

2. A process for forming tanning agents which comprises the simultaneous primary reactions in solution in an organic solvent and in the presence of hydrogen chloride of a polyhydric phenol with an alkyl nitrile and hydrogen cyanide and the concurrent condensation of the primary reaction products.

3. A process for forming tanning agents which comprises the simultaneous primary reactions in solution in an organic solvent and in the presence of hydrogen chloride of a. polyhydric phenol with acetonitrile and hydrogen cyanide and the concurrent condensation of the primary reaction products.

4. A process for forming tanning agents which comprises bringing together in solution in an organic solvent a polyhydric phenol, acetonitrile and a metallic cyanide, and passing l-ICl through the solution to liberate hydrogen cyanide from the metallic cyanide and to catalyze simultaneous primary reactions of the polyhydric phenol with the nitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

5. A process for forming tanning agents which comprises bringing together in solution in ether resorcinol, acetonitrile and zinc cyanide, maintaining the solution at the reflux temperature of ether and passing hydrogen chloride through the solution to liberate hydrogen cyanide from the zinc cyanide and to catalyze simultaneous primary reactions of the resorcinol with the acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

6. A process for forming tanning agents whic comprises bringing together in solution in ether phloroglucinol, acetonitrile and zinc cyanide,

maintaining the solution at the reflux temperature of ether and passing hydrogen chloride through the solution to liberate hydrogen cyanide from the zinc cyanide and to catalyze simultaneous primary reactions of the phloroglucinol with the acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

7. A process for forming tanning agents which comprises bringing together in solution in ether pyrogallol, acetonitrile and zinc cyanide, maintaining the solution at the reflux temperature of ether and passing hydrogen chloride through the solution to liberate hydrogen cyanide fromthe zinc cyanide and to catalyze simultaneous primary reactions of the pyrogallol With the acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

8. A process for forming tanning agents which comprises bringing together in solution in ether catechol, acetonitrile and zinc cyanide, maintaining the solution at the reflux temperature of ether and passing hydrogen chloride through the solution to liberate hydrogen cyanide from the zinc cyanide and to catalyze primary reactions of the catechol with the acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

9. A process for forming tanning agents which comprises bringing together in solution in ether hydroquinone, acetonitrile and zinc cyanide,

6. maintaining the solution at the reflux temperature of ether and passing hydrogen chloride through the solution to liberate hydrogen cyanide from the zinc cyanide and to catalyze simultaneous primary reactions of the hydroquinone with the acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products.

10. A tanning agent comprising the product of the simultaneous primary reactions of a polyhydric phenol with an alkyl nitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

11. A tanning agent comprising a solution in an inert organic solvent of the product of the simultaneous primary reactions of polyhydric phenol with an alkyl nitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

12. A tanning agent comprising a solution in an inert organic solvent of the product formed by the simultaneous primary reactions of resorcinol with acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

13. A tanning agent comprising a solution in an inert organic solvent of the product formed by the simultaneous primary reactions of phloroglucinol with acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

14. A tanning agent comprising a solution in an inert organic solvent of the product formed by the simultaneous primary reactions of pyrogal- 101 with acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

15. A tanning agent comprising a solution in an inert organic solvent of the product formed by the simultaneous primary reactions of catechol with acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

16. A tanning agent comprising a solution in an inert organic solvent of the product formed by the simultaneous primary reactions of hydroquinone with acetonitrile and hydrogen cyanide and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

17. The method of tanning hides which comprises contacting the hide with the product of the simultaneous primary reactions of a polyhydric phenol with hydrogen cyanide and an alkyl nitrile and concurrent condensation of the primary reaction products in the presence of hydrogen chloride.

18. The method which comprises tanning dried hides having a moisture content of from 10% to 15% by contacting them With a solution in an inert organic solvent of the product of the simultaneous primary reactions of a polyhydric phenol with hydrogen cyanide and an alkyl nitrile and concurrent condensation of the primary reaction products in the presence of hydrogen chloride and thereafter contacting th hide with water.

19. The method of tanning hides which comprises contacting the hide with an aqueous solution of the product of the simultaneous primary reactions of a polyhydric phenol with hydrogen cyanide and an alkyl nitrile and concurrent con- 7 8 densation of the primary reaction products in the Houben, Ber. Deut. Chem, Volume 59, B, page presence of hydrogen chloride. 2878-91 (1926).

Houben et al., Ber. Deut. Chem., Volume 60 B, References Cited in the file of this patent pages 53 t 00 19 7 UNITED STATES PATENTS 5 I-Iouben et a1., Ber. Deut. Chem., Volume 60 B,

pages 1759 to 1778 (1927). Number Name Date Kortzynski at 2.1., Chem, Abstracts, Volume 22,

987 750 Seyewetz Mar. 28 1911 page 4518 (1928). 2233949 schlack 1941 Houben et 3.1., Chemical Abstracts, Volume 24,

FOREIGN PATENTS 10 page 91 (1930). Adams et al. Org. Reactions Volume 5 Number Country Date 455,695 Great Britain Oct. 21, 1936 pages 388 397 455,697 Great Britain Oct. 21, 1936 OTHER REFERENCES 15 JALCA, June 1949, pages 418 and 419, abstract of Noerr et al., Colloquiumsber. Inst. 

1. A PROCESS FOR FORMING TANNING AGENTS WHICH COMPRISES BRINGING TOGETHER A POLYHYDRIC PHENOL WITH BOTH AN ALKYL NITRILE AND HYDROGEN CYANIDE AND CAUSING THEM TO REACT IN THE PRESENCE OF HYDROGEN CHLORIDE. 